1. Field of the Invention
The present invention generally relates to a reference electrode used as a standard electrode for a measuring electrode in the measurement of an ion-concentration of a solution. More specifically, the present invention relates to an improved sheet type or tube type reference electrode and an improved liquid junction.
2. Description of Related Work of the Inventors
Recently, the present inventors have developed an epoch-making sheet type electrode that exhibits various kinds of advantages. It can be remarkably small-sized, easily mass-produced, and remarkably low in the cost of production. It is also remarkably superior in operation and maintenance in place of electrodes for use in the measurement of ion-concentration (measuring electrodes, reference electrodes and composite electrodes thereof) of conventional type (test tube type) and various kinds of progressive improvements for them. They have been already disclosed in detail in many applications for patent and utility model by the present applicants, such as Japanese Utility Model application Ser. No. Sho 60-97385 and Japanese patent application Ser. No. Sho 61-285371.
As shown in FIG. 11, such a sheet type reference electrode (or a reference electrode portion in a sheet type composite electrode for use in the measurement of ion-concentration) has a gelatinized internal solution "g" enclosed in a support frame member "a" so that a liquid junction surface "b" of the gelatinized internal solution "g" may be exposed over a sample solution-dropping portion "c." An internal electrode "d" which is coated with an electrode material, such as AgCl, is formed so as to be brought into contact with the gelatinized internal solution "g." In addition, the gelatinized internal solution "g" is formed by adding a gelatinizer, such as agar-agar, and a water-evaporation inhibitor, such as glycerine, to a fundamental internal solution (for example, a 3.3 M-aqueous solution of KCl supersaturated with AgCl with a phosphoric acid buffer solution added). The details of the solution have been already disclosed in Japanese patent application Ser. No. Sho 61-63564 filed by the present applicants.
However, with the above described sheet type electrode, the liquid junction surface "b" of the gelatinized internal solution "g" is adapted to be directly brought into contact with the sample solution. Therefore, it is almost impossible to control the quantity of ions (K.sup.+, Cl.sup.-) which leak (diffuse) from the gelatinized internal solution "g" when used. Accordingly, a problem occurs in that the concentration of the gelatinized internal solution "g" is apt to be lowered in a comparatively short time. Since it is impossible to exchange the gelatinized internal solution "g", the useful life of the electrode as a whole is limited, and a problem of accuracy in measurement exists.